Manufacture of artificial leather



Patented Jan. I, 1935 UNITED STATES rmm PATENT orncr:

Company, Berlin, Maine N.H.,acorporatlonof No 1mm. apprise 3. 10:1.

This invention relates to the manufacture ,of artificial leathers into which fibrous material, for instance. in the form of pre-fabricated bibulous foundations, and liquid rubber, such as aqueous 5 rubber dispersions or rubber solutions, enter as raw materials. In making such leathers, it is sometimes the practice to impregnate the bibulous foundation of fiber with the liquid rubber, and then to dry, and, if desired, to vulcanize the impregnated product. One of the faults with artificial leathers thus made is that they are seriously weakened by exposure to water, particularly when liquid rubber in the form of an aqueous rubber dispersion, such as latex, has been used as the impregnating medium. Another defect is that they have what is known as a high permanent set, that is, a tendency to remain extended when stretched. These deficiencies, which stand out most conspicuously in the case of artificial leathers which have not been vulcanized or which have been only lightly vulcanized, must be removed, if the leather is to serve as "upper stoc in shoemaking, as such stock should properly have a low permanent set, in order to avoid deformation during the wear of the shoes, and, so too, should properly retain as much of its dry strength as possible when moistened. There are other uses which call for the properties of low permanent set and/or high wet strength in order to make possible a satisfactory substitution of an artificial leather for the natural product. A low permanent set is, for instance, highly desirable in upholstery, where, in order to avoid unsightly depressions in, say, the seat covering, the leather must return as completely as possible to its original dimensions when the weight of the sitter is removed. Low permanent set and high wet strengths are also of importance in automobile tops, especially where the leather may be put under considerable stress, as in a roadster or touring car where the top is constructed, so that it can be put down or up" as desired.

While the problem of producing satisfactory artificial leathers is prevalent when various kinds of fibrous foundations are utilized as the carrier sheets for the rubber, it exists in connection with one of the foundations sometimes considered most adaptable and most economical for the manufacture of artificial leathers, namely, the flexible and flufiy types of webs realized by interfelting cellulose fibers of the character of refined wood pulp on machinery of the papermaking type, but on which the web undergoes little compacting or squeezing as it undergoes conversion from aqueous suspension into the dry sheeted state. Indeed,

foimdations of this latter type, being tender and highly absorptive of water to begin with. are apt to give much trouble on account of poor water resistance and high permanent set,'even after they have been converted into artificial leathers by impregnation with latex and drying.

I have carried on considerable investigation with a view toward improving the permanent set and resistance to weakening by water of artificial leathers of the class hereinbefore described. The line of investigation with which this invention is concerned devolves about the use of viscose, as well as liquid rubber, in the manufacture of artificial leathers in which fibrous material serves as the carrier sheet or skeleton for these binders which impart leather-simulating properties thereto. When this line of investigation was initiated, I added comparatively large amounts of viscose to latex, and was greatly pleased by the fact that when a bibulous web of interfeited cellulose fiber was impregnated with the mixture and then dried, the resulting product was greatly improved in its wet strength and had a comparatively low permanent set. I was, however, disappointed to find that certain of the other important qualities of the product were badly impaired. Thus, the product was hard and brittle and was fatally deficient in its tear resistance. I pursued the investigation further by gradually reducing the amount of viscose added to the latex, and, much to my surprise and gratification, it was only when a comparatively trifling amount of viscose, in fact, less than approximately 1% of cellulose in the form of viscose, was present in the impregnated product along with the rubber, that my efforts proved fruitful. That with such an exceedingly small addition of viscose the product was phenomenally improved, in such properties as wet strength and permanent set without suffering noteworthy depreciation in other important respects was hardly to be predicted. This improvement ensues especially in the case of bibulous webs of interfeited fiber and without the necessity of subjecting the product to a vulcanizing operation, which is an expensive and fussy procedure, involving, as it does, careful compounding as well as heating or curing under closely regulated conditions. The viscose probably appears as regenerated cellulose in the final product, owing to the decomposition which goes on when the impregnated foundation is dried under the elevated temperature conditions customarily employed in commercial operation. It is possible that the sulphur which splits off from the viscose has a vulcanizing effect on the rubber,

view of the comparatively slight amount of sulphur in combination with the quantity of viscose employed.

It is, of course, possible to practice my invention using different types of fibrous foundations and incorporating various proportions of rubber thereinto. In any case, however, the proportion of rubber in the impregnated foundation is vastly greater than that of the viscose. I shall therefore instance only a typical example of procedure in which a bibulous web of interfelted fiber has undergone impregnation with an impregnating liquid in the form of latex containing added viscose under conditions to produce a finished product containing 1% regenerated cellulose and 45% rubber. The procedure may perhaps be best represented in tabular form, alongside of a procedure which was carried out similarly but with the absence of viscose in the latex. Here are the procedures:

Percent rubber in impregnating liquid 18% 18% Percent soluble cellulose in impregnating liquid added in form of viscose 0. 45 Basis weight original web 125 129 Percent fiber in finished sheet.... 45.? 43.? Thickness leather 0 035 0. 038 Average internal ply adhesion. M0 294 Tensile strength.-- 41 3 44. 5 Tensile stretch. 35. 6 D 13. 7% Permanent set... 16. 8 o 5. 5% Tour resistance 240 230 Percent water absorbed in 24 hours 74. 4 103 W et tensile strength. l2. 5 21. 4 Wet tensile stretch- 81. 5 137 Wet permanent set 22. 6 21. 1

In the foregoing table, the permanent setindicates the amountby which the product fails to recover when stretched to the breaking point. The internal ply adhesion represents the resistance to de-plying of the product when it is split an artificial leather product in so far as concerns its permanent set and wet strength, without detracting appreciably from its other important characteristics, especially that of tear resistance. Equally important, the internal ply adhesion is enhanced by a noteworthy margin. Although the stretch figures indicate a large difference in ultimate stretch, if less viscose is used, the stretch increases and yet the permanent set may remain comparatively low. The table merely shows the general effect of adding viscose in slight amount to the impregnating liquid in accordance with my invention. If it is desired to offset the effect of the viscose in loweringthe stretch, this can be done by altering the proportion of rubber to viscose, the proportions of both to fiber, the density or compactness of the original web, etc. The artificial leather product of the present invention is easily pervious to water vapor, that is, permits breathing, takes a leather finish entirely satisfactorily, and, can be embossed to simulate the grain efiects of various kinds of natural leathers most effectively. It is of a flexibility such that it is eminently serviceable as shoeupper stock.

A product, made in accordance with my invention is also eminently useful as innersoling. The advantages in this connection are that, since the viscose increases the internal ply adhesion,

- but this vulcanizing effect must be rather small in it is possible to reduce the quantity of impregnating solids, especially rubber, in the innersole, thereby materially reducing the cost of manufacturing and yet maintaining the desired internal ply adhesion and not sacrificing any of the other desirable characteristics. The flexibility of the innersole stock should, of course, properly be much less than a shoe-upper stock; and this can be brought about partly by the use of a much thicker initial foundation or by plying two or more impregnated foundations and partly by the introduction of small quantities of agents, such as casein and lime, into the latex, which serve to render a given thickness of impregnated foundation stiffer.

From the commercial standpoint, my invention, although fortuitous, is of great value, since, quite aside from the securement of best all-round properties made possible thereby in the resulting product, the manufacturer of artificial leather is not handicapped by the factor of expense, such as would be the case if large quantities of the comparatively expensive viscose were necessary.

The example hereinbefore given is' based on the use of the viscose in admixture with waterdispersed rubber of the character of latex as the liquid for impregnating the bibulous foundation of interfelted fiber, followed by the drying of the impregnated foundation at elevated temperature. This procedure is exceedingly simple and does not represent a departure in broad principle from previous practice. As already indicated, the drying of the impregnated web at elevated temperature is conducive to a decomposition of the viscose into regenerated cellulose, but, in any event, the drying of theviscose or its ageing in the sheet tends to produce regenerated cellulose. The conjunctive application of the latex and the viscose to the fabricated foundation is, so far as I am aware, the preferred practice, having in mind not only simplicity and low cost, but also the excellent results secured thereby. The admixture with latex of viscose in the amount of about .045 (calculated as cellulose) based on the latex, gives a highly satisfactory impregnating liquid, in'so far as concerns penetrating power, when the latex is of 15% to 20% rubber content, more or less. These specific figures were given by way of illustration, because when the impregnating liquid is made in accordance therewith, no trouble is encountered in quickly and uniformly impregnating a fabricated foundation of loosely interfelted fibers made on a paper machine or, for that matter, any other type of analogous bibulous foundation. In this connection, it is to be observed that the amount of rubber and cellulose added to the foundation may be varied, depending upon the particular concen-' tration of rubber and viscose in the impregnated liquid and upon the extent of squeezing to which the impregnated foundation is subjected after about 45%, or even much more rubber, and only about 1% regenerated cellulose as a maximum.

The purpose of my invention is, in effect, to

enhance the physical qualities of the product; and this is realized by adding to the liquid rubber a surprisingly small amount of film-forming materiaLwhich functions perhaps by forming a more or less highly attenuated honeycomb structure in the foundation and thereby reinforcing the comparatively high percentage of rubber decreases the permanent set and increases the internal ply adhesion, the resistance to water, and the modulus of elasticity of the product, nevertheless, physically equivalent agents, such as gelatine; may be used, particularly when combined with a tanning agent, such as formaldehyde or hexamethylenetetramine, as I have found that they give effects somewhat similar to theviscose.

' What I claim is: i

1. An' artificial leather comprising a dried, bibulous webof unwoven cellulose fiber impregnated with a mixture of water-dispersed rubber of the character of latex and viscose, said viscose amounting to not more than about 1%' as a maximum, calculated as cellulose, of the weight .of such leather, said leather being easily pervious to water vapor and hence being possessed of "breathing qualities.

2. An artificial leather comprising a dried, bibulous web of loosely interfelted cellulose fiber impregnated with a mixture of viscose and dispersed rubber of the character of latex, said viscose amounting to not more than about 1% as a maximum, calculated as cellulose, of the weight of such leather, said leather being easily pervlousto water vapor and hence being possessed of breathing" qualities.

3. An artificial leather comprising a dried, bibulous web of loosely interfelted cellulose fiber impregnated with a mixture of viscose and dispersed rubber of the character of latex, said viscose amounting to not more than about 1% as a maximum, calculated as cellulose, of the weight of such leather, and said rubber being vastly in-excess of said viscose, said leather being easily pervious to water vapor and hence being possessed of breathing qualities.

4. A process which comprises impregnating a bibulous unwoven fibrous foundation with a mixture of water-dispersed rubber and viscose containing up toonly about 0.45% soluble cellulose, and drying the impregnated foundation.

, 5. A process which comprises impregnating a bibulous unwoven web of interfelted cellulose fiber with a latex-viscose mixture containing about 15% to 20% rubber and up to only about 0.45% soluble cellulose, and drying the impregnated foundation.

6. An artificial leather comprising abibulous web of unwoven cellulose fiber impregnated with rubber-and viscose, said viscose amounting to not more than about 1%v as a maximum, calculated as cellulose, of the weight of such leather, but said rubber impregnant being present in vastly greater proportion, said leather being easily pervious to water vapor and hence being possessed of breathing qualities.

7. An artificial leather comprising a bibulous web of feltedfiber impregnated with the dried residue of a mixture of rubber latex and viscose, said viscose amounting to not more than about 1% as a maximum, calculated as cellulose, of the weight of such leather, but said rubber impregnant being present in the amount of at least about of the weight of said leather, said leather being easily pervious to water vapor and hence being possessed of breathing qualities.

1 MILTON O. SCHUR. 

